In recent years, flat panel displays using various display elements have been developed and produced in the electronic and electric industries. Most of the displays are those given by sealing a display element in a glass or plastic cell. Representative examples of such displays include a liquid crystal (LC) display, an electroluminescent (EL) display and the like. Among them, the EL display is excellent in high luminance, high efficiency, fast response and the like and is attracting attention as a flat panel display of the next generation. Examples of the EL elements include inorganic EL elements and organic EL elements. The inorganic EL element has been put into practical use for a backlight of watch, and the like, but still has some technical problems in full-colorizing. The organic EL element is superior to the inorganic EL element in the high luminance, high efficiency, fast response and multi-color development but has low heat resistance, and its heat-resistant temperature is said to be in the range of about 80 to 120° C. Therefore, in the sealing of the organic EL display, there is a problem that a thermosetting epoxy resin cannot be completely cured by heating.
To solve such problems as mentioned above, an attempt to develop a photo-curable sealing agent capable of undergoing fast curing at low temperatures has been made. The photo-curable sealing agents are roughly classified as photo-radically curable sealing agents or cationically photo-curable sealing agents. The photo-radically curable sealing agent has an advantage that various acrylate monomers or oligomers are employable, but has high volume shrinkage and low adhesive force upon curing. Thus, in order to decrease the volume shrinkage, the number of the functional groups per unit weight of the sealing agent must be small, and thus various physical properties become limited. On the other hand, the cationically photo-curable sealing agent has lower curing shrinkage and higher adhesive force than those of the photo-radically curable sealing agent since it uses a ring-opening polymerization, nevertheless, further improvement has been required with respect to practical use. In the preparation of the flat panel display, in order to enhance the production yield, a process wherein several panels are formed and adhered onto a large glass substrate, and then the glass substrate is separated therefrom is provided. In this process, high stress is applied on the glass substrate, and hence there is a problem that in the case where the sealing agent has insufficient adhesive strength, delamination may occur. Further, sealing the organic EL element requires high moisture permeation resistance, as well as surface adhesion to the various members used in the organic EL element for preventing water from penetrating into the panel from the adhered surface.
Patent Document 1: JP-A No. 2001-139933
Patent Document 2: JP-A No. 2000-72853
Patent Document 3: JP-A No. 09-241603